CCleaner for Mac uses much of the same cleaning techniques used in CCleaner for Windows. This means that you get the same advanced cleaning of browsers that you are used to in the Windows version. It also cleans many other Mac only applications such as QuickTime Player.
In addition to this, it cleans some files related to the operating system such as update files that can take up a huge amount of space.
And don't forget that the cleaning rules are updated every month, so new apps are added regularly.